<?php
/**
 * This file contains classes implementing the queue feature.
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @link http://www.yiiframework.com/
 * @copyright 2008-2013 Yii Software LLC
 * @license http://www.yiiframework.com/license/
 */

/**
 * CQueue implements a queue.
 *
 * The typical queue operations are implemented, which include
 * {@link enqueue()}, {@link dequeue()} and {@link peek()}. In addition,
 * {@link contains()} can be used to check if an item is contained
 * in the queue. To obtain the number of the items in the queue,
 * check the {@link getCount Count} property.
 *
 * Items in the queue may be traversed using foreach as follows,
 * <pre>
 * foreach($queue as $item) ...
 * </pre>
 *
 * @property Iterator $iterator An iterator for traversing the items in the queue.
 * @property integer $count The number of items in the queue.
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @package system.collections
 * @since 1.0
 */
class CQueue extends CComponent implements IteratorAggregate, Countable
{
    /**
     * internal data storage
     * @var array
     */
    private $_d = array();
    /**
     * number of items
     * @var integer
     */
    private $_c = 0;

    /**
     * Constructor.
     * Initializes the queue with an array or an iterable object.
     * @param array $data the initial data. Default is null, meaning no initialization.
     * @throws CException If data is not null and neither an array nor an iterator.
     */
    public function __construct($data = null)
    {
        if ($data !== null)
            $this->copyFrom($data);
    }

    /**
     * @return array the list of items in queue
     */
    public function toArray()
    {
        return $this->_d;
    }

    /**
     * Copies iterable data into the queue.
     * Note, existing data in the list will be cleared first.
     * @param mixed $data the data to be copied from, must be an array or object implementing Traversable
     * @throws CException If data is neither an array nor a Traversable.
     */
    public function copyFrom($data)
    {
        if (is_array($data) || ($data instanceof Traversable)) {
            $this->clear();
            foreach ($data as $item) {
                $this->_d[] = $item;
                ++$this->_c;
            }
        } elseif ($data !== null)
            throw new CException(Yii::t('yii', 'Queue data must be an array or an object implementing Traversable.'));
    }

    /**
     * Removes all items in the queue.
     */
    public function clear()
    {
        $this->_c = 0;
        $this->_d = array();
    }

    /**
     * @param mixed $item the item
     * @return boolean whether the queue contains the item
     */
    public function contains($item)
    {
        return array_search($item, $this->_d, true) !== false;
    }

    /**
     * Returns the item at the top of the queue.
     * @return mixed item at the top of the queue
     * @throws CException if the queue is empty
     */
    public function peek()
    {
        if ($this->_c === 0)
            throw new CException(Yii::t('yii', 'The queue is empty.'));
        else
            return $this->_d[0];
    }

    /**
     * Removes and returns the object at the beginning of the queue.
     * @return mixed the item at the beginning of the queue
     * @throws CException if the queue is empty
     */
    public function dequeue()
    {
        if ($this->_c === 0)
            throw new CException(Yii::t('yii', 'The queue is empty.'));
        else {
            --$this->_c;
            return array_shift($this->_d);
        }
    }

    /**
     * Adds an object to the end of the queue.
     * @param mixed $item the item to be appended into the queue
     */
    public function enqueue($item)
    {
        ++$this->_c;
        $this->_d[] = $item;
    }

    /**
     * Returns an iterator for traversing the items in the queue.
     * This method is required by the interface IteratorAggregate.
     * @return Iterator an iterator for traversing the items in the queue.
     */
    public function getIterator()
    {
        return new CQueueIterator($this->_d);
    }

    /**
     * Returns the number of items in the queue.
     * @return integer the number of items in the queue
     */
    public function getCount()
    {
        return $this->_c;
    }

    /**
     * Returns the number of items in the queue.
     * This method is required by Countable interface.
     * @return integer number of items in the queue.
     */
    public function count()
    {
        return $this->getCount();
    }
}
